Method and apparatus for generating a low frequency pulse in a wellbore

Abstract

A pressure pulse tool includes a tool housing, a valve disposed in the housing and having first and second valve components that are each rotatable relative to the housing and that cooperate to open and close a fluid flow path through the valve. The tool may include first and second power section coupled to the first and second valve components, respectively, for rotating the respective valve components. The power sections may each include a turbine rotor and the first and second rotors may have different geometries or may be powered by different amounts of fluid flow therethrough. Flowing fluid through the tool generates a pressure pulse having a desired pressure pulse frequency that may be lower than the first or second turbine rotor would generate alone.

What is claimed is: 
     
       1. A pressure pulse tool comprising:
 a tool housing; 
 a valve disposed in the housing, the valve having a first valve component and a second valve component; 
 a first power section mechanically coupled to the first valve component and configured to rotate the first valve component in response to fluid flow through the first power section; and 
 a second power section mechanically coupled to the second valve component and configured to rotate the second valve component in response to fluid flow through the second power section; 
 wherein the first and second valve components are each independently rotatable relative to the tool housing; and 
 wherein during operation the first and second valve components cooperate to open and close a fluid flow path through the valve at a desired frequency by rotating at different rates. 
 
     
     
       2. The pressure pulse tool of  claim 1  wherein the valve comprises a rotary plate valve, the first and second valve components being first and second valve plates, wherein each of the first and second valve plates includes one or more flow apertures. 
     
     
       3. The pressure pulse tool of  claim 2  wherein the first valve plate further including one or more relief ports. 
     
     
       4. The pressure pulse tool of  claim 1  wherein the valve comprises a rotary valve, the first valve component being an inner rotor and the second valve component being a sleeve, the sleeve including one or more flow apertures, the rotor including one or more lobes positioned to block the flow apertures for a portion of the rotation of the inner rotor relative to the sleeve. 
     
     
       5. A pressure pulse tool comprising:
 a tool housing; and 
 a valve disposed in the housing, the valve having a first valve component and a second valve component; 
 a first power section mechanically coupled to the first valve component and configured to rotate the first valve component in response to fluid flow through the first power section; and 
 a second power section mechanically coupled to the second valve component and configured to rotate the second valve component in response to fluid flow through the second power section for rotating the second valve component; 
 wherein the first and second valve components are each independently rotatable relative to the tool housing; 
 wherein the first and second power sections are each selected from the group consisting of positive displacement motors, and turbines. 
 
     
     
       6. The pressure pulse tool of  claim 5  wherein the first and second power sections are each a turbine and wherein the first and second turbines have different flow-to-rotation ratings and wherein the difference between the flow-to-rotation rating of the first power section and the flow-to-rotation rating of the second power section is selected so as to cause the tool to generate a pulse having a desired pressure pulse frequency at a selected flow rate. 
     
     
       7. The pressure pulse tool of  claim 6  wherein the valve includes a fluid passage positioned to allow fluid flowing through the tool to bypass one of the first and second turbines. 
     
     
       8. A method for transmitting a pressure pulse in a fluid, comprising:
 a) providing a pressure pulse tool, the pressure pulse tool including:
 a tool housing; 
 a valve disposed in the housing, the valve having a first valve component and a second valve component, the first and second valve components being each independently rotatable relative to the tool housing and cooperating to open and close a fluid flow path through the valve; and 
 a first power section mechanically coupled to the first valve component for rotating the first valve component in response to fluid flow and a second power section mechanically coupled to the second valve component for rotating the second valve component in response to fluid flow; 
 wherein the first and second power sections have different flow-to-rotation ratings; and 
 wherein the difference between the flow-to-rotation rating of the first power section and the flow-to-rotation rating of the second power section is selected so as to cause the tool to generate a pulse having a desired pressure pulse frequency at a selected flow rate; 
 
 b) flowing a fluid through the pressure pulse tool; 
 c) rotating the first valve component at a first rotation rate; 
 d) rotating the second valve component at a second rotation rate that is different from the first rotation rate; and 
 e) generating a pressure pulse with the valve in the drilling fluid, the pressure pulse having a pressure pulse frequency. 
 
     
     
       9. The method of  claim 8  wherein the tool further comprises a fluid passage positioned to allow drilling fluid to bypass at least one power section and step b) comprises flowing a portion of the drilling fluid through the fluid passage and not through the bypassed power section. 
     
     
       10. The method of  claim 8  wherein the first and second power sections are turbines and wherein step b) further includes bypassing one of the power sections with a portion of fluid that flows through the tool. 
     
     
       11. The method of  claim 8  wherein the pressure pulse frequency is less than 30 Hz. 
     
     
       12. The method of  claim 8  wherein the pressure pulse frequency is less than 15 Hz. 
     
     
       13. The method of  claim 8  wherein the ratio of the pressure pulse frequency to the frequency at which the valve would open if only one valve component were rotating is less than 1:5. 
     
     
       14. The method of  claim 8  wherein step d) includes providing a first amount of power to rotate the first valve component and providing a second amount of power to rotate the second valve component, wherein the first and second amounts of power are different. 
     
     
       15. The method of  claim 8  wherein the pressure pulse is used to reduce friction in the hole. 
     
     
       16. A method for transmitting a pressure pulse in a fluid, comprising:
 a) providing a pressure pulse tool, the pressure pulse tool including:
 a tool housing; 
 a valve disposed in the housing, the valve having a first valve component and a second valve component, the first and second valve components being each independently rotatable relative to the tool housing and cooperating to open and close a fluid flow path through the valve; and 
 a first power section mechanically coupled to the first valve component for rotating the first valve component and a second power section mechanically coupled to the second valve component for rotating the second valve component 
 
 b) flowing a fluid through the pressure pulse tool and bypassing one of the power sections with a portion of fluid that flows through the tool; 
 c) rotating the first valve component at a first rotation rate; 
 d) rotating the second valve component and a second rotation rate that is different from the first rotation rate; and 
 e) generating a pressure pulse with the valve in the drilling fluid, the pressure pulse having a pressure pulse frequency
 further including the step of selecting the volume of the bypassed portion so as to cause the tool to generate a pulse having a desired pressure pulse frequency at a selected flow rate.